Jury shown power of replica rucksack blasts

High-speed video footage showing replicas of the July 21 rucksack "bombs" exploding at a test site was played to Woolwich crown court yesterday.

On the silent film jurors saw a white flash fill the screen. In the centre an orange-red fireball appeared before dust and smoke billowed from the bottom of the device and a mushroom cloud blew out from the top.

Clifford Todd, who carried out the tests, said he and others hid in a bunker behind a hill 400 yards away from the detonation.

Asked if he could hear the blast, he said: "Yes, absolutely, you do hear it. You could feel the shockwave."

The blast destroyed the metal plate and chair under the bomb and tore away a plate five metres away, the court heard.

Describing the footage, Mr Todd, head of the scientific team at Fort Halstead, Kent, pointed out what he called a bell-shaped shimmer in the air during the explosion. "That is the shockwave produced by the main explosive."

The team tested combinations and concentrations of hydrogen peroxide and chapati flour - the materials the prosecution says were used in the bombs. Mr Todd said the ratio and concentrations of materials allegedly used on July 21 successfully exploded on every occasion.

"What you had was a viable high explosive using flour and hydrogen peroxide. If the concentrations and ratios were right, it could be detonated with just a detonator," Mr Todd told the court.